In a solar cell, carriers (electrons and holes) generated by photo irradiation to a photoelectric conversion section composed of a semiconductor junction or the like are extracted to an external circuit to generate electricity. In a heterojunction solar cell provided with a silicon-based thin-film and transparent electrode on a single-crystalline silicon substrate, providing a collecting electrode (metal electrode as an auxiliary electrode) is provided on a surface of the transparent electrode layer to improve current extraction efficiency.
A general solar cell is a double-sided electrode type solar cell including a collecting electrode for one conductivity-type (e.g., p-type) on a light-receiving surface, and a back electrode for opposite conductivity-type (e.g., n-type) on a back surface. The collecting electrode on the light-receiving side of the double-sided electrode type solar cell generally includes a plurality of finger electrodes for collecting photocarriers generated by light incidence, and a relatively thick bus bar electrode for extracting photocarriers collected in the finger electrodes to outside.
A plurality of solar cells are electrically connected to modularize the solar cells. In modularization of double-sided electrode type solar cells, the bus bar electrode provided on the light-receiving side is connected to the back electrode of the adjacent solar cell through an interconnector such as a tab line to establish series connection.
Further enhancement of efficiency of a solar cell module is expected, and reduction of an optical loss, improvement of module reliability, and so on are required. A region where collecting electrodes such as finger electrodes and a bus bar electrode are formed on the light-receiving side of a solar cell does not contribute to power generation because light is not incident to a photoelectric conversion section due to shading. Thus, it is required to reduce a shading loss caused by these electrodes, particularly a bus bar electrode.
A so-called back electrode type solar cell has been developed for reducing a shading loss caused by an electrode provided on a light-receiving surface. In the back electrode type solar cell, both a p-type electrode and an n-type electrode are formed on a back surface. Patent Document 1 suggests modularization of back electrode type solar cells using a wiring sheet. However, production of a back electrode type solar cell is more difficult and requires higher costs as compared to a double-sided electrode type solar cell.
Patent Document 2 discloses a solar cell in which bus bar electrode (main grid electrode) is not formed and only finger electrodes (sub-grid electrodes) are formed on a light-receiving surface, and in which a connection electrode such as a metal wire is formed on areas other than the light-receiving surface (e.g., on the lateral surfaces and a back surface). By connecting finger electrodes to the connection electrodes, the shading area on the light-receiving side can be reduced. As a technique similar to that in Patent Document 2, Patent Documents 3 and 4 each suggest forming an end surface electrode using a paste at one end of each of the solar cells and connecting mutually adjacent solar cells each other on the back side of each of the adjacent solar cells. In the solar cells in Patent Documents 2 to 4, photocarriers collected in finger electrodes on the light-receiving side are extracted to outside through the connection electrode and the end surface electrode. Accordingly, it is not necessary to provide a bus bar electrode having a large shading area on the light-receiving surface, and thus a shading loss caused by a collecting electrode on the light-receiving side can be reduced.